The long-term objective of this research is to define the chemical reactions and enzymatic processes involved in the energy metabolism of amino acid-fermenting anaerobic bacteria. Anaerobic bacteria are active in a variety of oxygen-free environments of medical interest such as the oral cavity and digestive tracts of man and animals, and in some systems of waste and sewage disposal. THe specific objectives of this proposal are: (1) determination of the enzymatic reactions involved in the reduction of aromatic amino acids to propionic acid derivatives by Clostridium sporogenes, and (2) determination of enzymatic reactions responsible for the conversion of tyrosine to p-cresol by Clostridium difficile. The investigation of aromatic amino acid reduction will concentrate on the enzymatic conversion of aromatic Alpha-hydroxy acids to Alpha-Beta unsaturated acids, a reaction that has not as yet been observed in this system. When conditions are found that permit the study of this reaction in cell extracts, the relevant enzyme(s) will be purified and characterized. The reduction of Alpha-Beta unsaturated acids will also be investigated to determine the extent of participation of CoA thiolesters in the process. The study of cresol formation will concentrate on the enzymology of the conversion of p-hydroxyphenolacetic to p-cresol, a reaction for which there is already some evidence. Conditions favorable for the formation of p-cresol from tyrosine and p-hydroxyphenyl-acetic acid by cell-free extracts will be determined and the responsible enzymes purified and characterized.